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Half bridge power supply, running on single rail DC?
Half bridge power supply, running on single rail DC?
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Old 3rd November 2017, 10:36 PM   #1
Djmagnum is offline Djmagnum  Switzerland
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Default Half bridge power supply, running on single rail DC?

Hey guys first time posting on here. I dont know as much as most of you so go easy on my question. I needed some help on how to understand split rail voltage supplies.

I want to make this PA speaker portable, instead of having an AC wall plug in it to only work. I am working with a 300 watt class D audio amplifier, I measured the voltages. I have 45.8 volts on VCC+ to VCC- and vise versa, and ground says 22.89 volts to VC+ and VC-.

The capacitors are rated at 50V on the amp board, so that tells me 45.8 is the highest voltage this thing sees? and since ground reference I think positive and negative side swing 22 volts from reference.

the problem is I cannot simply just connect the positive 45 to VCC+ and leave VCC- with 0.


So my question is, can I feed the 45 in the Power supply board where the transformer and rectifier circuits would invert the AC to DC, and let the board pre configure the voltages instead of me just jumping the wires to the amp selection?

there are other circuits like the bluetooth and display that take their own voltages, not sure how im going to make this happen. But it would be very cool to make this happen. I have some pictures too if anyone of you is willing to point out certain sections of the board to me. thank you again.
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Old 3rd November 2017, 11:02 PM   #2
MAAC0 is offline MAAC0  Portugal
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You can't just leave one of the rail voltages unconnected. That would require half voltage biasing for the ground reference. With small currents for preamps for example You can make a voltage doubler, but here it doesn't work. You would have to redesign the circuit schematic.


The simplest way of making it portable would be to use two 24V batteries one for each rail, and leave out the rectifier.
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Old 3rd November 2017, 11:38 PM   #3
Djmagnum is offline Djmagnum  Switzerland
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So have 24+ volts on both VCC+ and VCC-? would that work. 24 volts for each rail
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Old 4th November 2017, 04:35 AM   #4
PRR is offline PRR  United States
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Four truck batteries. Series.

Even then, a 300W amp won't play long until the batteries are flat.
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Old 4th November 2017, 04:38 AM   #5
Djmagnum is offline Djmagnum  Switzerland
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I have lithium ion high drain INR batteries to take care of that, but I guess my problem now is figuring out how the board also has a 12 and 15 volt out from the power supply circuit. I know taps in the transformer can do this, you can have multiple levels of voltage. But are these taps of 12 and 15 volts on the other side where the rectifier is? I'm wondering if they are AC or D.C.
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Old 5th November 2017, 10:42 PM   #6
MAAC0 is offline MAAC0  Portugal
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PRR


Why four Batteries ? He only needs 24V per rail. Truck is usually 24V


Positive Amp Rail ---- Plus (24V Battery) Minus- ----- Ground ----- Plus (24V Battery) Minus- ----- Negative Amp Rail


Djmagnum


An amp usually has 3 supply wires +- and Ground. If there are other connections, it is for the preamp or protection circuit perhaps.




Can You post as schematic or a photo of the PSU or the amp supply connections ?
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Old 5th November 2017, 11:22 PM   #7
Djmagnum is offline Djmagnum  Switzerland
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https://1drv.ms/f/s!AgW00phGkrhbyVSDouAQ5LScWdVI

That's the picture of it. I cannot find any schematic, these are cheap cheap speaker brands. Can't even find the amp or components on google search either.
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Old 6th November 2017, 03:29 AM   #8
PRR is offline PRR  United States
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Quote:
Originally Posted by MAAC0 View Post
Truck is usually 24V
Small truck. My Chevy 2500 is 12V, but battery is big. (My 1967 tractor has a bigger 12V batt.)

They don't let me play with 24V trucks.

Sorry for the confusion.
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Old 12th November 2017, 05:59 AM   #9
basreflex is offline basreflex  Spain
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the other option is buy a car audio booster that has built in stepup converters, usually cheaper than multiple batteries. check out some 12V 2ch ones with advertised powers > 1500W. at least these should have the stepup circuits. the power rating is usually overstated...
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Old 12th November 2017, 11:15 AM   #10
infinia is offline infinia  United States
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Consider a inverter and/or generator. \One with and one without storage batteries.
You could beg borrow or steal one to see how this goes over. I'm sure everyone in Switzerland has access to these things. LOL

Otherwise if you could build a ~300 VDC battery boost thingy you could modify the front end of the power supply in the picture & let your SMPS do the rest. but besides investing OUR time plus the risks of directing others hacking batteries uhh ...i'll get back with you.
you can do some home work figuring out Li battery sizes from W* hours and run times involved, you will soon turn back to option 1 or 2.
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Last edited by infinia; 12th November 2017 at 11:21 AM.
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